Objective: To determine the short- and long-term effectiveness of the muscle energy technique (MET) compared with corticosteroid injections (CSIs) for chronic lateral epicondylitis (LE). Design: Randomized controlled trial with 1 year of follow-up. Setting: Outpatient clinic of a university's department of physical medicine and rehabilitation. Participants: Patients with chronic LE (N=82; 45 women, 37 men). Interventions: Eight sessions of MET, or a single CSI was applied. Main Outcome Measures: Grip strength, pain intensity, and functional status were assessed using the pain-free grip strength (PFGS), a visual analog scale (VAS), and the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire, respectively. Measurements were performed before beginning treatment and at 6, 26, and 52 weeks afterward. Results: When the baseline PFGS, VAS, and DASH scores were compared with the scores at the 52-week follow-up, statistically significant improvements were observed in both groups over time. The patients who received a CSI showed significantly better effects at 6 weeks according to the PFGS and VAS scores, but declined thereafter. At the 26- and 52-week follow-ups, the patients who received the MET were statistically significantly better in terms of grip strength and pain scores. At 52 weeks, the mean PFGS score in the MET group was significantly higher (75.08±26.19 vs 62.24±21.83; P=.007) and the mean VAS score was significantly lower (3.28±2.86 vs 4.95±2.36; P=.001) than those of the CSI group. Although improvements in the DASH scores were more pronounced in the MET group, the differences in DASH scores between the groups were not statistically significant. Conclusions: This study showed that while both MET and CSI improved measures of strength, pain, and function compared with baseline, subjects receiving MET had better scores at 52 weeks for PFGS and the VAS for pain. We conclude that MET appears to be an effective intervention in the treatment of LE.